Slip rings are widely used in equipment such as CT devices. An X ray source and detectors are generally secured onto a circular slip ring surrounding an object under detection. A sectional image of the detected object along the thickness direction is obtained as the slip ring rotates one round. In conventional CT devices, in order to obtain information of images from different view angles, it is required to rotate the slip ring and use information of location and rotation speed of the slip ring during its rotation. To this end, an encoder for slip ring has been designed. The main function of such encoder is to convert, through photoelectric encoding, the information of the location and rotation speed of the rotating slip ring into two orthogonal differential pulse signals with phases A and B, and a differential pulse signal with phase Z per rotation round, and transmit them to a host computer. The host computer analyzes the differential pulse signals with phases A, B and C to obtain the information of the location and rotation speed of the slip ring.
The accuracy and stability of the output signal from the encoder for slip ring are important to reliable and stable operation of the entire equipment. Having operated for certain time period, the coding belt of the encoder may have some holes partly or completely blocked due to, for example, accumulation of dust. This leads to output of erroneous differential pulse signals and abnormal control and operation of the equipment.
There is a need for an encoder and encoding method for slip ring, which can avoid or mitigate influence on output signals from partly or completely blocked holes, and improve operation stability of the entire equipment.